POS1011 DIFFERENT SYNOVIAL MACROPHAGE AND FIBROBLAST SUBSETS, EXPRESSION PROFILES AND CELL-CELL INTERACTIONS CHARACTERISE SEX DIFFERENCES IN CHRONIC INFLAMMATORY JOINT DISEASES
Authors: R. Micheroli, A. Khmelevskaya, C. Pauli, E. Vallejo-Yagüe, M. Elhai, K. Buerki, O. Distler, A. Ciurea, C. Ospelt
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Chronic inflammatory joint diseases differ between males and females in terms of disease manifestation, treatment response and radiographic progression. A molecular basis that could explain these differences has yet to be identified. <h3>Objectives</h3> The study aimed to find differences in synovitis at histology and transcriptome level between males and females with chronic inflammatory joint diseases. <h3>Methods</h3> Synovial tissue was obtained by ultrasound-guided biopsy from inflamed joints from 5 males and 5 age- and disease-matched females. Histological analysis included Krenn score and synovial pathotype. Single-cell RNA-sequencing (scRNA-seq) libraries were prepared with 10X Genomics and sequenced with NovaSeq 6000. We performed additional histological analyses (Krenn score and CD68 staining) on synovial tissue samples obtained from joint replacement surgery in 13 males and 13 age- and synovial pathotype-matched females with rheumatoid arthritis. The following R packages were used for bioinformatic analysis: Cell Ranger, Seurat, Harmony and CellChat. KEGG gene set enrichment analysis was performed with ClusterProfiler. <h3>Results</h3> We included 4 psoriatic arthritis, 2 rheumatoid arthritis, 2 undifferentiated arthritis and 2 peripheral spondyloarthritis patients. Females and males did not significantly differ in baseline characteristics: mean age was 46.2 years in females, 46.8 years in males; 2 knees and 3 wrists were biopsied per sex; mean swollen joint count was 6.8 in females and 8.2 in males. Histological analysis between the sexes showed no significant differences: synovitis was moderate in both sexes (mean Krenn total score 4.0) and pathotypes were balanced in males (1 diffuse-myeloid, 2 lympho-myeloid, 2 pauci-immune) and females (1 diffuse-myeloid, 1 lympho-myeloid, 1 pauci-immune, 2 ungradable). 41,014 cells were integrated for scRNA-seq analysis (female 21,636 and male 19,378 cells). Pseudobulk variance analysis showed a significant correlation of sex with principal component (PC) 3, accounting for 12.6% of the sample variation (Figure 1A). In addition to the sex-specific genes XIST and PRS4Y1, the following genes were main drivers of the PC3 variation: H19, CXCL9 and CXCL10. Diagnosis was not significantly associated with any PC. Comparison of the individual cell cluster proportions showed that LYVE1<sup>pos</sup> macrophages (MC) were significantly more prevalent in females (4.9% in males versus 13.7% in females, p = 0.03) (Figure 1B). In confirmatory histological analysis, consistent with the known location of LYVE1<sup>pos</sup> MC in the lining layer, both Krenn lining score (mean (SD) score in males 1.85 (0.69) and 2.08 (0.76) in females) and CD68 lining score (mean (SD) score in males 1.77 (1.17) and 2.08 (0.95) in females) were higher in females but did not reach statistical significance. Differential gene expression analysis showed that mainly in synovial fibroblasts (SF) genes were differentially expressed between males and females (n = 1944). In SF, upregulated genes in males led to a significant enrichment of proinflammatory pathways (TNF pathway, NF-kappa B pathway, IL-17 pathway). In contrast, upregulated genes in females were significantly associated with ECM-receptor interaction, focal adhesion, protein digestion and absorption pathways (Figure 1C). In cell-cell interaction analyses, most outgoing signaling was observed in SF while MC represented most receiving cells; IL6 and CXCL signaling pathways were significantly enriched in males, and COLLAGEN and THY1 signaling pathways in females (Figure 1 D/E). <h3>Conclusion</h3> Our study shows potential important differences in synovitis between males and females with chronic inflammatory joint diseases. In females, synovitis was characterized by abundance of LYVE1<sup>pos</sup> MC and SF expressing extracellular matrix-associated genes. In contrast, male SF showed a proinflammatory transcriptional profile. These sex-specific differences should be considered in research studying synovitis and may warrant sex-specific therapeutic approaches. <h3>REFERENCES:</h3> NIL. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Raphael Micheroli: None declared, Alexandra Khmelevskaya: None declared, Chantal Pauli: None declared, Enriqueta Vallejo-Yagüe: None declared, Muriel Elhai Consultant of: BMS, Grant/research support from: Support for travel (Janssen), Kristina Buerki: None declared, Oliver Distler Consultant of: Abbvie, Adrian Ciurea: None declared, Caroline Ospelt: None declared.